Reciprocating fluid motor and valve control therefor



April 3, 1956 H. T. DINKELKAMP ETAL 2,740,384

RECIPROCATING FLUID MOTOR AND VALVE CONTROL THEREFOR Filed Dec. 4, 1953 2 Sheets-Sheet l April 1955 H. T. DlNKELKAMP ETAL RECIPROCATING FLUID MOTOR AND VALVE CONTROL THEREFOR 2 Sheets-Sheet 2 Filed Dec. 4, 1953 l a @mw'e 5 F i 4 m It? ll m 5 J /J 7 M 6 A l l |H I l lw U n w M w 2 w 5 7 w 0 6 J w l- J n a} z 5 IN 0 l J Q; 7Q M w WW Him \\w m mm 4 United States Patent RECIPROCATING FLUID MOTOR AND VALVE CONTROL THEREFOR Henry T. Dinkellramp, Niles, and Earl Feicht, Chicago, 111., assignors to Stewart-Warner Corporation, Chicago, 111., a corporation of Virginia Application December 4, 1953, Serial No. 396,283 10 Claims. ((21. 121-152) The present invention relates to reciprocating fluid motors for lubricant pumps and the like.

One object of the invention is to provide a reciprocating fluid motor in which the fluid force on the power piston is quickly reversed at opposite ends of the. piston stroke by the operation of an improved reversing valve energized by the operating fluid of the motor.

A more specific object is to provide an improved reciprocating pump of the above character in which a fast acting reversing valve energized by the operating fluid of the motor is released as an incident to the progression of the power piston to either end of its normal stroke to produce quick reversal of the fluid pressures on the piston.

Another object is to provide for a reciprocating fluid motor an improved, fast acting valve in which a fluid flow control member is shifted almost instantaneously from one operating position to another by a hammer-like blow struck by actuating means accelerated by the operating fluid of the motor.

A further object is to provide a reciprocating fluid motor with fast acting, valve actuating means of the character recited which is automatically and properly supplied with operating fluid as an incident to the direction of operating fluid to the main power cylinder.

Other objects and advantages will become apparent from the following description of the form of the invention shown in the drawings, in which:

Figure l is a longitudinal sectional view through a reciprocating pump motor incorporating the invention;

Fig. 2 is a vertical sectional view taken along the line 2-2 of Fig. 1, certain parts being broken away for clearness in illustration;

Fig. 3 is a fragmentary sectional view taken along line 3-3 of Fig. 1;

Fig. 4 is a fragmentary sectional view taken along line 4-4 of Fig. 1 and illustrating the power piston near the lower end of its stroke; and

Fig. 5 is a fragmentary sectional view on a somewhat enlarged scale taken generally along line 5--5 of Fig. l.

The fluid actuated pump motor incorporating the present invention comprises, as shown in Fig. 1, a hollow casing 10, a cylinder section 12 defining a cylinder 14 and bolted to the top of the casing which forms a lower head 15 for the cylinder, and an upper cylinder head 16 bolted to the upper end of the cylinder section. A power piston 18 of conventional construction is reciprocably mounted within the cylinder 14 and connected to a piston rod 20 that extends downwardly into the casing 10 through a suitable packing gland and bearing sleeve 22 in the lower cylinder head 15. The lower end of the piston rod 29 is connected to a pump rod 24 extending downwardly through the lower end of the casing 10 to a pump (not shown).

The side wall of the cylinder section 12 at one side of the cylinder 14 is thickened and bored to define two passageways 2'8 and 30 leading from the medial portion of the cylinder section to two recesses 32, 34, formed in 2,740,384 Patented Apr. 3, 1956 2* the upper and lower cylinder heads 16, 15 and communicating with opposite endsof the cylinder. I

An L-shaped. e haust outlet 36 (Se Figs. 1 and 3) extends horizontally through the thickened cylinder sec: tion wall to present an open end disposedibetween the adjacent ends of the two. passageways 2 8, '30.

The vertically aligned ends of the two passageways 28 and 30 and the exhaust outlet 36, which open outwardly through the side of the cylinder section 12, are covered by a port block 38 secured to the side wall of the cylinder section. The port block 38- defines an exhaust port 40, constituting in effect an outward continuation of the "exhaust outlet 36, and two control ports 42 and 44 diea valve casing 46 bolted to the side of the cylinder sec- 5 tion 12 and coacting with the port block 38 to define a fluid chamber 418. Compressed air or other suitable operating fluid is introduced into the chamber 48 through an inlet 50.

A generally rectangular D slide valve flow control member 52 is vertically slidable between upper and lower positions on the outer face of the port block 38, and is recessed and dimensioned to connect, the exhaust port 40 with either of the flow control ports 42, 44 to exhaust fluid from either end of the cylinder 14 while permitting a free flow of fluid under pressure through the other control port to the opposite end of the cylinder. Vertical movement of the flow control member 52 along the outer face of the pont block 33 is guided by a vertically slotted plate 56 and opposed spring pressed ball detents 58 mounted in holders'tiil on the plate 56 to cooperate with suitable depressions on opposite sides of the slide valve 52, as shown in Fig. 3.

To quickly reverse the movement of the power piston 18 at each end of its stroke, the slide valve 52 is shifted almost instantaneously from one operating position to another by valve actuating means 62 energized by the operating fluid of the motor. As shown, the valve actuating means 62 comprises elongated actuator 64 vertically disposed in the valve casing 46 and connected at opposite ends to two biasing pistons 66, 68 slidably disposed in two biasing cylinders 70, 72 in the upper and lower ends of the valve casing.

The actuator '64 itself comprises a vertical stem 74 extending longitudinally through a central member 76 and two cylindrical tubes 78 abnttingly engaging opposite ends of the central member. A lost motion connection between the actuator 64 and the flow control member 52 is formed by two vertically spaced shoulders 80 on the central member 76 which straddle a shifting lug 82 formed on the slide valve 52.

The biasing pistons 66, 63 on opposite ends of the elongated actuator 64 are of similar construction, each comprising a rubber-like ring 34 sandwiched between two washers 86 fitted onto the necked down outer end of the adjacent tube 73. The upper piston 66 is retained on the actuator 64 by a nut 88' threaded onto the upper end of the stem 74. In a similar manner, the lower biasing piston 68 is retained on the actuator by an elongated extension member 99 threaded onto the lower end of the stem 74 and pinned against loosening movement, as shown in Fig. 1.

The biasing cylinders 70, 72, which receive the respective biasing pistons 66, 68, are of similar construction. Each cylinder is formed bya sleeve 92 threaded into an outwardly opening bore 94 in the valve casing 46. The inner end of this sleeve engages a washer 96 encircling the actuator 64 and defining the inner end ofthe cylinder. The inner faceof the washer :96 engages tin-actuator guide 3 bushing 98 having a radial flange 100 resting against a circular ledge on the inner end of the valve casing bore 94. Suitable seals 104 and 106 are interposed between the guide bushing and the actuator 64 and between the bushing and the valve casing 46. A seal between the sleeve 92 and the valve casing bore 94 is formed by an O-ring 108. The outer end of the upper sleeve 92 is closed by a loosely fitting dust cap 110. I

The inner ends of the biasing cylinders 70, 72 thus 8 formed are connected by bores 112 and 114 to the respective passageways 28, 30 leading to opposite ends of the power cylinder 14. The outer ends of the bores 112, 114 intersect annular passageways 116, 118 formed by necking down the inner ends of the biasing cylinder sleeves 92 to be radially spaced from the adjacent side walls of the bores 94. One or more radial openings 120 in the inner end of each sleeve 92 connects the surrounding annular passageway with the inner end of the enclosed biasing cylinder.

The elongated actuator 64 is yieldably held in either of its extreme vertical positions by detent means comprising a pair of spring pressed plungers 122 mounted in the valve casing 46 and acting horizontally on retaining cams 124 on opposite sides of the central member 76 of the actuator. As best shown in Fig. 5, each of the retaining cams 124 defines a central, vertical land surface 126 merging at its upper and lower ends with inwardly sloping cam surfaces 128. The V-shaped inner end of each plunger 122 defines two cam follower surfaces 130.

As shown in Fig. 3, each plunger 122 is slidably mounted in a radially flanged bushing 132 positioned in the inner end of a countersunk bore 134 extending through a boss 136 on the valve casing 46. A locking screw 138 threaded into the side of the valve casing 46 extends radially through the bushing 132 into a longitudinal slot 140 in the plunger to prevent rotation of the plunger. An annular seal 142 encircling the plunger 122 and seated in the countersunk outer end of the bushing 132'is held in place by a second bushing 144 fitted into the bore 134 and slidably receiving the enlarged outer end 146 of the plunger. Another seal 148 which rings the enlarged end 146 of the plunger is held against the outer end of the second bushing 144 by a centrally bored cap 150 threaded into the outer end of the boss bore 134 and engaging a radial collar 152 on the second bushing 144 to hold this bushing and the previously mentioned bushing 132 solidly in place. Loosening of the cap 150 is prevented by a setscrew 154 threaded into the boss 136.

The plunger 122 is urged against its associated earn 124 by a coil compression spring 156 interposed between the inside of the cap 150 and the bottom of a bore 158 in the enlarged outer end of the plunger. The force of the spring 156 is supplemented by a differential force of operating fluid acting on the opposite ends of the plunger 122. For this purpose a smaller bore 160 is extended in wardly along the axis of the plunger 122 from the outer end bore 158 to connect with the previously mentioned plunger slot 140 which communicates with the fluid chamber 48. Fluid passing longitudinally through the plunger into the hollow cap 150 acts on the outer end of the plunger which is larger than the inner end of the plunger which protrudes into the chamber 48.

It will be noted that the clearance space 162 between the forward end of the enlarged portion 146 of the plunger 122 and an inwardly turned flange 164 on the second bushing 144 is vented through a radial opening 166 in the second bushing, a circular space 168 at the forward end of the bushing collar 152, and a port 170 in the boss 136.

Yieldably retained in either of its two extreme vertical positions by the action of the spring pressed plungers 122 on the cams 124, the actuator 64 is released for movement to its other extreme position upon movement of the power piston 18 to either end of its stroke. For this purpose a lost motion linkage 172 is connected to the depending extension member 90 of the actuator 64 to be operated by the power piston 18.

As shown in Figs. 1 and 2, the lost motion linkage 172 comprises a rocker lever 174 centrally supported on a pivot pin 176 extending transversely through a narrowed portion 171 of the motor casing 10 disposed under the valve casing 46. The rocker lever 174 itself isfashioned from a pair of spaced metal strips 180 held by a bolt 182 against opposite sides of a spacer block 184, which receives a transverse bushing 185 for the pin 176. A lost motion connection between the outer end of the rocker lever 174 and the lower end of the actuator extension memher is formed by two opposed buttons or contacts 186 bolted to the inner faces of the extreme outer ends of the lever strips 180 and engaging opposite sides of a necked down shank 188 extending downwardly from a shoulder 190 on the extension member 90 to an enlarged head 192. "The buttons 186 upon engaging either the shoulder 190 or head 192 transmit rocking movement of the lever 174 to the actuator 64.

At the inner end of the rocker lever 174, the strips 180 are spread to embrace an annular collar 194 slidably mounted on the piston rod 20 between the packing gland 22 in the casing 10 and a radially enlarged ring 196 fixed to the lower end of the piston rod. Vertical movements of the collar 194 are transmitted to the rocker lever 174 through two opposed contact buttons 198 fixed to the inner ends of the lever strips 180 and slidably disposed within an external annular groove 200 on the collar. The linkage 172 is assembled into the casing 10 through an open side of the casing normally covered by a removable metal sheet 208.

When the power piston 18 approaches its uppermost position, the ring 196 on the piston rod 20 engages the collar 194 to swing the rocker lever 174 in the clockwise direction (with reference to Fig. l) to impart an initial downward movement to the actuator 64. Similarly, the power piston 18 upon approaching the lower end of its stroke, as indicated in Fig. 4, engages two vertical pins 202 slidable in two sealed bushings 204 mounted in the upper end of the casing 10 on opposite sides of the piston rod 20. Forced downwardly by the piston 18, the pins 202 engage an annular flange 206 on the upper end of the collar 194, forcing the collar downwardly to impart an initial upward movement to the actuator 64.

To review the overall operation of the illustrated embodiment of the invention, the drawings show the positional relationship of the structural elements at the beginning of a downward stroke of the power piston 18. The flow control member 52 is in its lower operating position connecting the passageway 30 from the lower end of the cylinder 14 to the exhaust outlet 36. Operating fluid in the chamber 48 flows through the uncovered upper control port 42 and the passageway 28 into the upper end of the cylinder 14 to force the piston 18 downwardly.

Some of the operating fluid flows under pressure from the upper passageway 28 through the bore 112 into the upper biasing cylinder 70. Acting on the lower face of the upper biasing piston 66, this fluid urges the actuator 64 in the direction for shifting the flow control member 52 to its upper operating position to reverse the movement of the power piston 18. At this time the lower biasing cylinder 72 is connected with the exhaust outlet 36 through the bore 114 and the passageway 30.

Even though biased upwardly by operating fluid in the cylinder 70, the actuator 64 is held against upward movement by the spring pressed plungers 122 acting against the upper cam surface 128 of the retaining cams124. The effective area of each of the biasing pistons 66, 68 is so limited that the force of the operating fluid on either piston will not overcome the detent action of these plungers 122. Moreover, the supplementing of the biasing force of the plunger springs 156 by the pressure of operating fluid acting on the outer enlarged ends 146 of the plungers provides for adequate retaining action of the plungers when high fluid pressures are used without excessive retaining action when the operating fluid pressure isless.

This positional relationship of the control valve structure remains undisturbed until the power piston 18 approaches its lowermost position. Then the piston 18, acting through the pins 202, the collar 194, and lever 174, imparts an initial upward movement to the actuator 64 overcoming the retaining action of the spring pressed plungers 122. This initial upward movement of the actuator 64 does not disturb the position of the slide valve 52. It merely takes up some of the lost motion between the central actuator member 76 and the shifting lug 82 on the flow control member. Hence the flow of actuating fluid into the upper end of the cylinder 18 remains unrestricted.

However as soon as the detent plungers 122 have ridden up on the cam surfaces 128 onto the land surfaces 126, the actuator 64, freed of the retaining action of the plungers, is immediately shifted to its upper extreme position by operating fluid acting on the upper biasing piston 66. This movement of the actuator 64, which is energized by the operating fluid independently of the main power piston 18, produces an extremely rapid shifting of the flow control member 52 to its upper operating position to reverse the fluid forces on the piston 18.

In the preferred construction shown, the effective length of the respective retaining cam surfaces 128 along the axis of the actuator 64 (that is, the distance through which the actuator must be shifted longitudinally to be released from the opposed detent plungers 122) is somewhat less than the lost motion between the actuator shoulders 8i) and the coacting shifting lug 82 on the flow control member 52. Thus the actuator 64, energized by the operating fluid, picks up momentum after being released from the retaining action of the detent plungers 122 before engaging the flow control member 52. As a result, the flow control member 52 is shifted to its other operating position almost instantaneously by a hammerlike blow of the actuator 64. The fast action of this valve shifting movement is entirely independent of the speed of the power piston 18 and produces extremely rapid reversal in the direction of movement of the piston 18.

It will be understood that the actuator 64 is automatically retained in its upper extreme position by the detent plungers 122 acting on the lower retaining cam surfaces 128. Upward shifting of the flow control member 52 for the main piston 16 automatically exhausts operating fluid from the upper biasing cylinder 70 and directs fluid under pressure into the lower biasing cylinder 72 in preparation for shifting the actuator to its lower position to again reverse the power piston.

While we have shown and described a preferred embodiment of our invention, it will be apparent that numerous variations and modifications thereof may be made without departing from the underlying principles and scope of the invention. We therefore desire, by the following claims, to include all such variations and modifications by which substantially the results of our invention may be obtained through the use of substantially the same or equivalent means.

We claim:

1. In a reciprocating fluid motor, the combination of a shiftable flow control member having two operating positions, an actuator for said flow control member movable between two extreme positions to shift said flow control member from one operating position to another, piston means connected to said actuator, cylinder means receiving said piston means, means serving as an incident to movement of said flow control member into one operating position to direct fluid into said cylinder means to urge said piston means and said actuator in a direction for shifting the flow control member to its other operating position, detent means for retaining said actuator in either Cal of said two extreme positions against the force of fluid on said actuator piston means, and fluid motor operated means for releasing said detent means to free said actu ator to shift said new control member to its other operating position.

2. In a reciprocating fluid motor having a cylinder and a power piston therein, the combination of a shiftable flow control member for reversing the power piston, a reciprocable actuator having a lost motion connection to said flow control member, means for yieldably retaining said actuator in either of its two extreme positions and including a cam on said actuator defining two cam surfaces and a spring pressed plunger engageable with either of said cam surfaces, piston means connected to said actuator, biasing cylinder means receiving said actuator piston means, means serving as an incident to movement of said flow control member into one operating position to direct fluid into said biasing cylinder means to urge said actuator in the direction for shifting said flow control member to its other operating position, and lost motion linkage means connecting said power piston with said actuator to overcome the retaining action of said spring pressed plunger on said cam as an incident to movement of the power piston to either end of its normal stroke.

3. In a reciprocating fluid motor having a power cylinder, a piston slidably mounted within said cylinder, means defining fluid passageway-s to opposite ends of said cylinder, means defining an exhaust outlet, and means defining an inlet for fluid under pressure, fast acting control valve means comprising, in combination, a flow control member shiftable between two operating positions to direct operating fluid to either end of the motor cylinder and to exhaust fluid from the other end of the cylinder, valve actuating means movable reversely from one extreme position to another, means forming a lost motion connection between said actuating means and said flow control member, said actuating means including biasing piston means and biasing cylinder means slidably receiving said biasing piston means, means connecting said biasing cylinder means with opposite ends of the power cylinder of the motor so that the admission of fluid under pressure to said biasing cylinder means as an incident to the supplying of fluid under pressure to either end of the power cylinder upon movement of said flow control member to one operating position serves to bias said piston means in a direction to shift the flow control member to its other operating position, detent means coacting with said actuating means to yieldably retain the latter in either of its two extreme positions against the force of fluid on said biasing piston means, and lost motion means connecting said valve actuating means with the main piston of the motor whereby the latter upon approaching either end of its stroke releases said valve actuating means to shift said flow control member to its other operating position.

4. In a pump motor having a power cylinder and a piston slidably mounted within said cylinder, control valve means comprising, in combination, a flow control member shiftable between two operating positions to direct fluid under pressure to either end of the cylinder and exhaust fluid from the opposite end of the cylinder, a valve actuating member shiftabl'e between two extreme positions and coacting with said flow control member to shift the latter between its two operating position-s, yieldabl'e detent means coacting with said valve actuating member to retain the latter in either of its extreme positions, biasing cylinder means, means providing fluid communications between said biasing cylinder means and opposite ends of the power cylinder of the motor, biasing piston means connected with said valve actuating member and slidably mounted in said biasing cylinder means, the relationship of said biasing pi-ston means to said flow control member and of said biasing cylinder means to said fluid communication means being such that the admission of fluid under pressure to said biasing cylinder means as an incident'to the supplying of fluid under pressure to either end of the power-cylinder upon movement of said flow control member to one operating position serves to bias said piston means in a direction for shifting said flow control member to its other operating position, the eflective piston areas of said actuating piston means exposed to fluid under pres sure in said biasing cylinder means being insuflicient to overcome the retaining action of said detent means, yet sufficient to produce quick shifting movement of said actuating member; and lost motion means connecting said valve actuating member with said power piston whereby the latter upon approaching either end of its stroke overcomes said detent means releasing said actuator member for shifting movement by fluid in said biasing cylinder means.

5. A reciprocatory pump motor comprising, in combination, a power cylinder, a main piston slidably mounted in said cylinder, means defining passageways leading to opposite ends of said cylinder, means defining an exhaust outlet, means defining an inlet for fluid under pressure, a shiftable flow control member coacting with said passageways to connect said inlet with either end of said cylinder and connect said exhaust outlet with the opposite end of said cylinder, an elongated actuating member shiftable between two extreme positions and having a lost motion connection with said flow control member, pistons on opposite ends of said actuating member, two cylinders receiving said respective actuating member pistons and communicating substantially continuously with the respective ends of said power cylinder, detent means for yieldably retaining said actuator in either of said extreme positions, said detent means including retaining cam surfaces having effective longitudinal extensions along said actuating member somewhat shorter in length than the lost motion between said actuating member and said flow control member, and linkage means connecting said actuator member with said power piston whereby the latter upon approaching either end of its stroke releases said actuator from said detent means.

6. In a reciprocating fluid motor the combination of a cylinder, a power piston slidable within said cylinder, a shiftable flow control member for reversing said piston, a reciprocable actuator for shifting said control member from one operating position to another, a symmetrical cam member on said actuator defining a pair of inclined cam surfaces, a spring pressed plunger engageable with either of said cam surfaces to retain said actuator in either extreme position, means for supplying motor operating fluid to the outer end of said plunger to increase the force of the latter on said cam with increasing fluid pressures, biasing piston means connected to said actuator, biasing cylinder means receiving said biasing piston means, means supplying operating fluid to said biasing cylinder means to urge said actuator in opposite directions, and lost motion means connecting said actuator with said power piston whereby movement of the latter to either end of its stroke overcomes the force of said plunger on said cam to release said valve actuator for shifting movement.

7. In a reciprocating fluid motor, the combination of a cylinder, at power piston slidable within said cylinder and having a piston rod extending therefrom, fluid supply means including a flow control member movable between two operating positions for reversing said piston, a shiftable actuator for said flow control member movable between two working positions, piston means connected to said actuator, cylinder means receiving said actuator piston means, means for directing fluid into said actuator cylinder means when said flow control member is in one position to urge said actuator piston means in a direction for shifting said flow control member toward its other position, detent means for yieldably retaining said actuator in either of its working positions against the force of fluid on said actuator piston means, a rocker connected for eflective enagement with said actuator and having another portion disposed adjacent said piston rod, means on said piston rod engageable with said rocker upon movement of said piston to one end of its normal stroke, and reciprocable means in said first mentioned cylinder engageable with said rocker and with said power piston upon movement of the latter to the other end of its normal stroke.

8. A reciprocatory fluid motor comprising, in combination, a main cylinder, a main power piston in said cylinder fluid supply means including passageway means and a flow control member shiftable from one operating position to another to direct fluid under pressure into either end of said cylinder while exhausting fluid from the other end of the cylinder depending upon the position of the flow control member, reversible fluid actuating means connected to shift said flow control member from one operating position to another, fluid means for supplying fluid to said fluid actuating means as an incident to movement of said flow control member to either operating position to energize said actuating means for moving the flow control member back to its other operating position, detent means interconnected with said flow control member for retaining the latter in either operating position against the force of said fluid actuating means for the flow control member, and operating means interconnected With said detent means and positioned for actuation by said main piston as an incident to movement of the latter to either end of its stroke to temporarily release said detent means freeing said flow control member for movement by said fluid actuating means to its other operating position.

9. A reciprocatory fluid motor comprising, in combination, a main cylinder, a main power piston in said cylinder, fluid supply means including passageway means and a flow control member shiftable from one operating position to another to direct fluid under pressure into either end of said cylinder while exhausting fluid from the other end of the cylinder depending upon the position of the flow control member, reversible fluid actuating means connected to shift said flow control member from one operating position to another, means for supplying fluid to said fluid actuating means as an incident to movement of said flow control member to either operating position to energize said actuating means for moving the flow control member back to its other operating position, yieldable detent means connected with said flow control member for retaining the latter in either operating position against the force of said fluid actuating means for the flow control member, fluid pressure responsive means communicating with said fluid supply means and connected to said detent means to increase the effective retaining action of the latter proportionally to increases in the fluid pressure, and operating means interconnected with said detent means and positioned for actuation by said main piston as an incident to movement of the latter to either end of its stroke to temporarily release said detent means thus freeing said control member for movement by said fluid actuating means to its other operating position.

10. A reciprocatory fluid motor comprising, in combination, a main cylinder, a main power piston in said cylinder, fluid supply means including passageway means and a flow control member shiftable from one operating position to another to direct fluid under pressure into either end of said cylinder while exhausting fluid from the other end of said cylinder depending upon the position of the flow control member, reversible fluid actuating means connected to shift said flow control member from one operating position to another, means for supplying fluid to said fluid actuating means as an incident to movement of said flow control member to either operating position to energize said actuating means for moving the flow control member back to its other operating position, yieldable detent means interconnected with said flow control member for retaining the latter in either operat- 1% ing position against the force of said fluid actuating means References Cited in the file of this patent therefor, and operating means arranged for actuation hy UNITED STATES PATENTS sald main power system and lnterconnected Wlth said actuating means for supplementing the force thereof on 94973 Post sePt' 1869 the detent means to overcome the latter as the main 5 290,063 Kessler 1883 526,149 Farley Sept. 18, 1894 piston moves to either end of its stroke.

2,437,391 Klein et a1 Mar. 9, 1948 

